Pentagon Mountain is an 8,873-foot peak in Montana’s Bob Marshall Wilderness, managed by Flathead National Forest. The highest point in the Trilobite Range, it rises steeply above Pentagon Creek and stands about two miles west of the Continental Divide. Its runoff reaches two drainage systems, flowing south and west to the Spotted Bear River and north to the Middle Fork Flathead River. The mountain lies in a subarctic climate with severe winters and short summers. Its sedimentary rocks, laid down from the Precambrian to the Jurassic, were later shaped by the Lewis Overthrust, a major geologic event in the northern Rockies.